Analysis of the geomagnetic activity of the D_st index and self-affine fractals using wavelet transforms

H. L. Wei (1) , S. A. Billings (1) , M. Balikhin (1)

1 Department of Automatic Control and Systems Engineering

The geomagnetic activity of the D_st index is analyzed using wavelet transforms and it is shown that the D_st index possesses properties associated with self-affine fractals. For example, the power spectral density obeys a power-law dependence on frequency, and therefore the D_st index can be viewed as a self-affine fractal dynamic process. In fact, the behaviour of the D_st index, with a Hurst exponent H?0.5 (power-law exponent ??2) at high frequency, is similar to that of Brownian motion. Therefore, the dynamical invariants of the D_st index may be described by a potential Brownian motion model. Characterization of the geomagnetic activity has been studied by analysing the geomagnetic field using a wavelet covariance technique. The wavelet covariance exponent provides a direct effective measure of the strength of persistence of the D_st index. One of the advantages of wavelet analysis is that many inherent problems encountered in Fourier transform methods, such as windowing and detrending, are not necessary.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Sciences de la Terre

H. L. Wei, S. A. Billings, M. Balikhin. Analysis of the geomagnetic activity of the D_st index and self-affine fractals using wavelet transforms. Nonlinear Processes in Geophysics, 2004, 11 (3), pp.303-312. ⟨hal-00302336⟩